Also to note: for most programs (including Ai), nested paths made to create "holes" are 'compound' paths. For example text (converted to shapes) such as a "D" or "0" (but not an "L") or any path shapes to make "logical" holes.

You can export a compund path from Ai...works well in Carrara; don't think I ever did that in Hex and maybe Hex does not understand a compound path...but good to know for most any other 3D program.

Don't have .ai, so don't know about the compound curves - I took the OP at his word and imagined two whole curves, as I get in Gimp and InkScape. Anyhow, I traced his inner curve in Hex, offset it and used Ruled surfaces, no problem:)

Can be a bit of a nuisance untangling the overlapping points, but it is do-able, although your method is less hassle.

A variation on your method that I use for these difficult shapes is to extrude and bridge - adding points where necessary to avoid cross-overs and to be sure of getting only quads - just a thing I have about tri's:)

A variation on your method that I use for these difficult shapes is to extrude and bridge - adding points where necessary to avoid cross-overs and to be sure of getting only quads - just a thing I have about tri's:)

For a simple shape as shown in example, then not much work. But what if you had an imported AI file with thousands of points with multiple holes. Would you really take the time to attempt all quads unless specifically asked for (needed)?

A variation on your method that I use for these difficult shapes is to extrude and bridge - adding points where necessary to avoid cross-overs and to be sure of getting only quads - just a thing I have about tri's:)

For a simple shape as shown in example, then not much work. But what if you had an imported AI file with thousands of points with multiple holes. Would you really take the time to attempt all quads unless specifically asked for (needed)?

If, like me your hobby doesn't justify the expense of Illustrator, you can draw shapes in Inkscape, save as .svg (scalable vector graphics) and convert to .ai using Uniconverter (both free Opensource). This converts to .ai 5, which is compatible with Hex.